A conventional electric water heater as shown in FIG. 1 includes: a storage tank S having an electric heating coil H and a thermostat T mounted in the tank S, whereby the cold water is fed into the tank through a feed pipe F and the heated or warm water is discharged through the discharge pipe D mounted on a top portion of the tank when heated by the heating coil H and controlled at a constant temperature by the thermostat T.
However, when an appreciable volume of hot water (V) is consumed from the tank S, the cold water will be instantly supplied into the tank and will not be immediately heated to the desired warm temperature, causing a delayed heating of the water and also causing unpleasant feeling for the user such as someone waiting for washing his hair in a barber shop especially in a cold weather or winter season.
The present inventor has found the drawbacks of the conventional water heater and invented the present water heater sensitively responsive to temperature variations.